1. Field of the Invention
The invention relates to paving machines and, more particularly, relates to a method and apparatus for improving the operation of a machine for paving hot mix asphalt or the like by facilitating hopper loading, improving the feed of materials to the distributing auger, and improving the composition of materials fed to and/or distributed by the distributing auger.
2. Discussion of the Related Art
Paving machines are well known for receiving paving materials such as hot mix asphalt (HMA), distributing the paving materials onto a roadway or another surface, and working the materials into a mat. Such machines typically include a self-propelled tractor-like vehicle having a chassis; an engine mounted on the chassis for propulsion and for material distribution functions; a hopper mounted on the chassis; a helical screw type distributing auger mounted near the rear of the chassis; and a heated vibratory screed mounted on the chassis behind the distributing auger.
The hopper, typically having a capacity of about 12 tons, is relatively low to the ground and extends all the way to the front of the paving machine so as to be capable of receiving HMA directly from a truck positioned in front of and pushed by the paving machine as the paving machine travels along the roadway. Hoppers of this type are incapable of feeding HMA by gravity to the distributing auger mechanism and thus require an internal conveyor mechanism to convey materials from the front of the hopper to a rear discharge opening located adjacent the distributing auger mechanism. This conveyor mechanism typically takes the form of a pair of parallel drag slat conveyors extending longitudinally of the hopper and communicating with independently operable feeder gate mechanisms located at the discharge opening.
In use, HMA is discharged from the hopper in one or more windrows in front of the distributing auger as the chassis travels in a forward direction. The distributor auger then distributes and levels the windrowed HMA, and the screed then compacts the distributed material into a mat.
Three problems arise from discharging materials onto the ground in front of the distributing auger as described above.
First, it is difficult to resume paving from the end of a previously-paved segment. If the distributing auger and screed are placed at the end of the previously-paved segment, the HMA conveyor delivers materials at a location which is spaced from the previously-paved segment. The resulting gap between the materials and the end of the previously-paved segment cannot adequately be filled by the distributing auger, resulting in a rough transition area between paved segments. This drawback can be partially alleviated by positioning the discharge point of the HMA conveyor directly in front of the distributing auger. However, a significant gap and resulting rough area still remain.
Second, HMA materials tend to become segregated by weight and particle size when they are stored in and conveyed out of the hopper. Conventional conveyors pile this partially segregated HMA in front of a distributing auger, which then spreads the materials without significant remixing. Indeed, materials at the bottom of the windrows may not be disturbed by the distributing auger. This spreading without significant remixing may result in a poorer quality paved surface.
Third, it is relatively difficult to maintain a uniform discharge of materials from the hopper using such conveyors, particularly when the hopper is nearly empty during which time less or even no materials are delivered to the discharge opening between the times at which successive flights of the conveyors reach the openings. Substantial hand work is required at the end of the mat to compensate for this deficiency and to deliver to the discharge openings any materials which are inaccessible by the conveyors. The problem of uneven feed of materials from the hopper can be partially alleviated by permitting the speeds of the parallel drag slat conveyors to be independently controlled by the operator(s) as disclosed in U.S. Pat. No. 3,453,939 to Pollitz et al. Such a control system, however, necessarily increases further the cost and complexity of the paving machine and also places additional burdens on the operators.